1. Field of the Invention
The invention relates to an electric machine of the rotary current type, whereby in a casing a stator is fitted with at least one stator winding and at least two mechanically separate rotors, whereby the rotors have the same axis of rotation, and whereby each rotor has electromagnetic interaction with the electromagnetically active stator, whereby the rotor speeds may be the same or different.
2. Discussion of Background Information
It is known that rotary current machines can be used advantageously for electromechanical energy transformation. These are fitted with a stator and rotary current winding system through which electric current flows, and have interaction with a magnetic field that is created either by permanent magnets, by field windings in the case of synchronous machines, or by the stator winding itself in asynchronous and reluctance machines, or by a combination of these possibilities.
The manufacture of the known electromechanical drives or purely mechanical drives, for example gears in which two different, usually independent speeds are required, is very complicated.
From EP-A-798844, an electric machine of the rotary current type is known, which in a casing has a stator with at least one stator winding and at least two, mechanically separate rotors. The rotors have the same axis of rotation, and each rotor has electromagnetic interaction with the electromagnetically active stator, whereby the rotor speeds may be the same or different.
Furthermore, from WO-A-9218346, DE-A-3313768 and GB-A-2278242, electric machines are known whereby in a casing a stator is fitted with at least one stator winding and at least two mechanically separate rotors.
From D3 WO-A-9201532, a work spindle drive for a tool machine is known, which has several adjustable speeds. In this drive, two electric motors are arranged one after the other on the same axis, whereby each electric motor is fitted with a choke with phase control for adjusting the infinitely variable speed. Each choke acts only on one electric motor.
Last but not least, from EP-A-817359 an electric motor is known, which has a stator and two rotors on one axis, and which can be used as a vehicle drive.
All the electric machines mentioned above have the disadvantage, however, that for the generation and use of two different speeds or torques they require two stator windings and two current rectifiers, which means that they require more space and more expensive hardware.
The aim of the invention is to create an electric machine that avoids the above disadvantages and with which two, usually independent speeds can be realised, such as required for example in the drives of motor vehicles or in piston engines.
The invention is characterised by the fact that the supply of at least one of the windings is provided by superposition of at least two rotary field components, one for each rotor, controlled by the motor control.
With this invention, it is for the first time possible to produce an electric drive system that can be manufactured and used economically. This offers the surprising advantage that the control of two electrically powered rotors running at different speeds is possible with relatively simple hardware and, preferably, with one stator winding and only one supplying electronic power system. Of particular advantage thereby is that fact that compared with the known solutions only about half as many electric components and windings are required.
A further advantage of this invention is the fact that, unlike the known electromagnetic drives or purely mechanical drives, such as gears in which two different, usually independent speeds are required, major parts such as the stator plate package, the casing elements, parts of the Controls, Can be spared. The drive system according to the invention can be used for example in pump/fan combinations, e.g. in oil burner drives or cooling systems, motor/motor fan combinations, or as a drive with differential shafts with two mechanical outputs. Moreover, mechanical gears with variable transmission can be realised electrically, from and to which electric power can also be fed by means of a mechanical-electric-mechanical converter. For example, in this way a drive for a motor vehicle with gear function, clutch function, starter function and integrated power generation can be realised. Furthermore, vibration torques on one gear side, such as those generated in piston engines, can be compensated by periodical electric power in- and output via the electric intermediate stage.
In accordance with a particular feature of the invention, the stator has two separate windings, whereby each winding is supplied by a source of electric power, preferably with independent control, and each winding has electromagnetic interaction with at least one rotor. The advantage of this array with two independent windings lies in the fact that both parts of the engine can be controlled entirely independent of each other, and that they have only very little influence on each other.
In accordance with a special feature of the invention, at least one of the windings of the stator is designed as a groove or air-gap winding. The advantage thereby is that these windings can be manufactured rationally.
In accordance with a further feature of the invention, at least one rotor is designed as an inner rotor and/or at least one rotor is designed as an outer rotor. With this design, a compact engine model is possible.
In accordance with a further feature of the invention, the rotors and the stator are arranged in accordance with the principle of a disc-type rotor. Thereby, the two windings as groove or air-gap windings are located on the left and right of the disc-type stator. Accordingly, the rotors are also designed as disk-type rotor with permanent magnet excitation, cage rotor, reluctance structure, etc., on the left and right of the stator. The two stator winding systems are in turn supplied by two generally separate power sources.
In accordance with a special design of the invention, the stator has one winding, whereby this winding generates a magnetic field with at least two marked rotary frequency components that have selective electromagnetic interaction with the rotors. The advantage of this design lies in the fact that one winding and its corresponding supply, preferably an inverter, can be spared, and the two frequency components are already superimposed on the signal side by two motor part controls, and supplied by a common power part via the drive. The price for this advantage is a higher loss and vibration torque, but this is often acceptable in return for the more economic drive.
In accordance with a further feature of the invention, the electric power is fed to or from the windings of the stator via electronic power modules, such as transistor, GTO inverter, diode rectifier and the like. The advantage thereby is that with the current state of the art this technology guarantees perfect function.
In accordance with a further design of the invention, at least two rotors are linked via at least two windings and an electronic power module as an electric gear. The design of the double or multiple rotor machine as a gear offers the possibility of smooth speed transmission with simple controllability via an electric intermediate stage. Moreover, it provides a coupling function if required, whereby the system is uncoupled if a power part is not enabled.
In accordance with a further design of the invention, electric power can be exchanged with an electric system via the electric gear intermediate stage. Thereby it is of advantage that electric power can be drawn from the electric intermediate circuit in addition, in order to realise an electric power supply. Moreover, with the electric power supply a temporarily or permanently increased mechanical performance can be provided at the gear output.
In accordance with a further feature of the invention, the rotors are designed as differential gear. Advantageously, a differential gear function can be realised by preferably electric power supply and bilateral mechanical drawing of power.
In accordance with a further design of the invention, a common electronic power input module and a number of electronic power output modules corresponding to the number of windings are provided, which are controlled by the motor control. Thus, torque fluctuations at one of the mechanical inputs of the gear can be compensated by electric power supply and discharge or be generated arbitrarily, for example in a vibration or breakaway function.
In accordance with a further feature of the invention, there is a speed-selective start-up procedure for the rotors. The two rotors of the double rotor machine enter into interaction selectively with different rotary field components of the rotary field in terms of frequency, and therefore run at usually different speeds. The selection of frequencies can be made for example with different moments of inertia, brakes that can be released depending on time, or different rotor types.
The invention is explained in more detail based on the design examples illustrated in the figure.